This invention relates generally to improvements in power tools for use in the installation of threaded fasteners, particularly such as threaded fasteners of the type used in the aerospace and related industries. More specifically, this invention relates to improvements in a fastener installation tool of the general type disclosed in U.S. Pat. No. 5,553,519, including a power-driven socket for installing a threaded nut onto the shank of a threaded fastener, in combination with a fixture pin for normally engaging and retaining the threaded fastener against rotation during power-driven nut installation. The improved fastener installation tool includes a simplified spring-loaded clutch assembly for accommodating limited fixture pin rotation in response to a torque overload condition, thereby protecting the fixture pin against undesired deformation damage or breakage.
A variety of specialized fasteners have been developed and are widely used in the aerospace and related industries, wherein these specialized fasteners have been designed to meet specific design criteria and uses. One example of such specialized threaded fastener comprises a threaded bolt adapted for power-driven installation of a threaded nut onto the bolt shank, without requiring access to the bolt head. That is, such fasteners are designed to fit through a preformed opening in a substrate or other panel-like structure with the bolt head inaccessibly disposed at a blind side thereof. The bolt shank protrudes through the substrate opening with a threaded end exposed for screw-on installation of the threaded nut. The shank end of the bolt is formed to include a small shallow recess of typically hexagonal shape for receiving a mating key used to retain the bolt against rotation as the threaded nut is installed.
Power-driven installation tools are known for use in installing such fasteners. Such fastener installation tools include a power-driven socket for receiving and supporting the threaded nut, and for rotatably driving the threaded nut onto the threaded bolt shank. A generally coaxially positioned fixture pin is also included and carries a key such as a hex key or the like for slide-fit reception into the shallow recess formed in the end of the bolt shank. The fixture pin is normally retained against rotation relative to the power-driven socket, whereby the fixture pin normally retains the threaded bolt against rotation during the nut installation process. Some fastener installation tools of this type further include clutch means for permitting at least some fixture pin rotation in response to a torque overload condition to protect the fixture pin and key against undesired bending or breaking. One example of such power-driven fastener installation tools is shown and described in U.S. Pat. No. 5,553,519, which is incorporated by reference herein.
More particularly, in a typical fastener application using a power-driven installation tool of the above-described type, the key on the fixture pin engages and supports the fastener shank against rotation as the power-driven socket rotatably drives the nut onto the threaded bolt shank. During this step, the fixture pin and key are progressively retracted axially into the tool relative to the socket, in order to remain fully seated within the fastener end recess as the nut is rotatably advanced onto the bolt shank. At least some friction between the bolt and the substrate assists the fixture pin in retaining the fastener against rotation during nut installation. In some installations, however, particularly such as in the case of composite material substrates in aircraft and the like, friction may contribute minimally to bolt retention during nut installation. Accordingly, the fixture pin and key may comprise the primary or sole structure for preventing bolt rotation during nut installation. Torque loads between the power-driven socket and the bolt can sometimes be transmitted directly to the fixture pin and key, resulting in over-torquing and bending or breaking thereof. When this occurs, it is necessary to remove the installation tool from service for appropriate repair or replacement.
U.S. Pat. No. 5,553,519 shows and describes a spring-loaded clutch assembly for safeguarding the fixture pin and key against damage in response to a torque overload condition. However, the clutch assembly comprises a relative complicated structure consisting of multiple assembled components adapted to protect against torque overload damage while still accommodating fixture pin retraction as the power-driven socket is advanced to rotatably install a threaded nut onto the bolt shank.
There exists, therefore, a need for further improvements in and to fastener installation tools of the type having a fixture pin disposed coaxially within a power-driven socket, particularly with respect to providing a simplified spring-loaded clutch assembly for protecting the fixture pin against torque overload damage. The present invention fulfills these needs and provides further related advantages.